The present disclosure relates to a pilot pressure control system. Moreover, the present disclosure relates to a method for supplying a pilot pressure to a pilot inlet of a control valve.
A control valve of a hydraulic control circuit may be controlled by adjusting a pilot signal pressure at one or more pilot inlets of the control valve. To this end, the hydraulic control circuit may include an electric proportional valve, such as a solenoid valve, that receives an electric control signal and supplies a pilot signal pressure, indicative of the electric control signal, to one of the pilot inlets of the control valve.
Purely by way of example, a hydraulic circuit, such as the one that has been described hereinabove, may be used in a steering system for an articulated vehicle such as a wheel loader or an articulated hauler. Such a hydraulic circuit may allow a driver of the articulated vehicle to control the steering of the articulated vehicle by means of a control member, such as a joystick, which via electrical signals communicates with solenoid valves of the hydraulic control circuit such that the solenoid valves in turn control the pilot signal pressures of the pilot inlets of the control valve. As such, the above hydraulic circuit presents a steer-by-wire possibility to the driver.
However, there is a risk that an incorrect electronic communication occurs between the control member and the solenoid valves. Moreover, there is a risk that a solenoid valve as such is impaired which in turn results in that it does not operate as desired. As such, a vehicle adapted to be operated by a steer-by-wire system is often also provided with a second hydraulic steering system, e.g. a steering system comprising a steering wheel and an orbitrol, in order to increase the reliability of the vehicle's steering.
In order to increase the accuracy of a control valve that is operated by means of pilot signal pressures produced by electronic proportional valves, US2006/0117942 A1 proposes that displacement sensors be installed on the ends of the control valve. The displacement sensors may be used for determining whether or not the control valve is in normal operation and, if it is not, modifying the control signal to the electronic proportional valves such that a requested condition of the control valve is nevertheless obtained.
Although the US2006/0117942 A1 control circuit provides an appropriate level of reliability for many applications, it may nevertheless be desired to increase the reliability further.
It is desirable to provide a pilot pressure control system that has an appropriate reliability level.
As such, the present disclosure relates, according to an aspect thereof, to a pilot pressure control system for controlling a pilot signal pressure at a pilot inlet of a control valve. The pilot pressure control assembly comprises a pilot outlet adapted to be connected to the pilot inlet.
According to an aspect of the present disclosure, the pilot pressure control assembly further comprises a first pilot valve assembly and a second pilot valve assembly. Each one of the first and second pilot valve assemblies is individually controllable so as to selectively provide a first fluid flow direction from a pressure line to the pilot outlet and a second fluid flow direction from the pilot outlet to a drain line. At least the first pilot valve assembly is adapted to assume a maximum pressure supply condition so as to supply a first pilot valve assembly maximum pressure Pmax to the pilot outlet. At least the second pilot valve assembly is adapted to provide a pressure drop from the pilot outlet to the drain line via the second pilot valve assembly.
Moreover, the pilot pressure control system is configured such that, when the pilot pressure control system is connected to the pressure and drain lines and when the first pilot valve assembly is controlled so as to assume the maximum pressure supply condition and the second pilot valve assembly provides a fluid flow in the second fluid direction with a minimum pressure drop, the pressure at the pilot outlet is equal to or above 20% of the first pilot valve assembly maximum pressure. Alternatively, the pressure may be equal to or above 30% of the first pilot valve assembly maximum pressure.
By virtue of a pilot pressure control system according to the above it is ensured that even if the second pilot valve assembly malfunctions such that is inadvertently provides a minimum pressure drop to the drain line, e.g. by inadvertently providing a maximum opening to the drain line, the pilot pressure control system as a whole will nevertheless still be able to provide an appropriately large pressure to the pilot outlet. This in turn implies that the pilot pressure control system will still be able to change the condition of the control valve to which it is connected.
Optionally, when the first pilot valve assembly is controlled so as to assume the maximum pressure supply condition and the second pilot valve assembly provides a minimum pressure drop, the pressure at the pilot outlet is equal to or less than 80% of the first pilot valve assembly maximum pressure. Alternatively, the pressure at the pilot outlet is equal to or less than 70% of the first pilot valve assembly maximum pressure.
The feature that the pressure is equal to or below any one of the above limits implies that it may be possible to change the condition of the control valve to which the pilot pressure control system is connected even if the first pilot valve assembly malfunctions such that it inadvertently assumes a maximum pressure condition. By virtue of the fact that the pressure at a first pilot inlet that is associated with the malfunctioning first pilot valve assembly is below any one of the above discussed ranges, it is possible to change the condition of the control valve by applying a second pressure to a second pilot inlet, which second pressure essentially only needs to exceed a pressure of 80%, alternatively 70%, of the first pilot valve assembly maximum pressure. Purely by way of example, the condition of the control valve may be changed by applying a pressure that is approximately equal to the first pilot valve assembly maximum pressure to the second pilot inlet.
Optionally, the pilot pressure control system comprises a throttling arrangement adapted to throttle fluid flowing from the pilot outlet to the drain line via the second pilot valve assembly.
The above discussed throttling arrangement may be used in order to obtain a preferred minimum pressure drop over the second pilot valve assembly.
Optionally, the throttling arrangement is also adapted to throttle fluid flowing from the pressure line to the pilot outlet via the first pilot valve assembly.
The above discussed pressure line throttling arrangement may be used in order to obtain the maximum pressure at the pilot outlet.
A second aspect of the present disclosure relates to a pilot pressure control assembly for a control valve. The pilot pressure control assembly comprises a first pilot pressure control system according to the first aspect of the present disclosure for controlling, the pilot pressure at a first pilot inlet of the control valve. The pilot pressure control assembly further comprises a second pilot pressure control system according to the first aspect of the present disclosure for controlling the pilot pressure at a second pilot inlet of the control valve.
A pilot pressure control assembly according to the second aspect of the present disclosure may provide a relatively high reliability since such a control assembly increases the possibilities that the condition of the control valve may be changed even if one of the pilot valve assemblies of the pilot pressure control assembly does not function as desired. Moreover, a pressure control assembly according to the second aspect may be able change the position of the control valve, even in the event of a malfunctioning pilot valve assembly, without the need of firstly identifying a malfunctioning, valve and thereafter modifying the operation of the pilot pressure control assembly.
A third aspect of the present disclosure relates to a pressurized medium control system. The control system comprises a control valve which in turn comprises a pilot inlet. The pressurized medium control system further comprises a pilot pressure control system according to the first aspect of the present disclosure and/or a pilot pressure control assembly according to the second aspect of the present disclosure.
A fourth aspect of the present disclosure relates to a pressurized medium steering assembly for an articulated vehicle. The pressurized medium steering assembly comprises a pressurized medium control system according to the third aspect of the present disclosure and/or a pilot pressure control assembly according to the second aspect of the present disclosure and/or a pilot pressure system according to the first aspect of the present disclosure.
A fifth aspect of the present disclosure relates to a vehicle comprising a pilot pressure system according to the first aspect of the present disclosure and/or a pilot pressure control assembly according to the second aspect of the present disclosure and/or a pressurized medium control system according to the third aspect of the present disclosure and/or a pressurized medium steering assembly according to the fourth aspect of the present disclosure.
A sixth aspect of the present disclosure relates to a method for supplying a pilot pressure to a pilot inlet of a control valve using a pilot pressure control assembly. The pilot pressure control assembly comprises a first pilot valve assembly and a second pilot valve assembly. Each one of the first and second pilot valve assemblies is individually controllable so as to selectively provide a first fluid flow direction from a pressure line to the pilot inlet and a second fluid flow direction from the pilot inlet, to a drain line.
According to the sixth aspect of the present disclosure, the method comprises:                issuing individual control signals to each one of the first and second pilot valve assemblies,        for at least one of the first and second pilot valve assemblies throttling a fluid flow from the pilot inlet to the drain line.        
Optionally, the method further comprises:                for at least one of the first and second pilot valve assemblies, throttling a fluid flow from the pressure line to the pilot inlet.        
It should be noted that the appended drawings are not necessarily drawn to scale and that the dimensions of some features of the present invention may have been exaggerated for the sake of clarity.